Wires incorporating a helical component, assemblies thereof, and use of said assemblies as catalyzer and/or to recover precious metals

ABSTRACT

A wire comprising at least one helically wound wire element is disclosed. The helical winding consists of a platinoid or platinoid alloy wire (20). Also disclosed are assemblies of these wires (20) such as knitted materials, fabrics and felts, and the use of said assemblies as catalysers in the reaction for preparing nitric or cyanhydric acid, and to recover precious metals from these catalysers.

FIELD OF THE INVENTION

The present invention relates to novel threads containing at least oneelement in the form of a helical winding, to their assemblings,particularly in the form of woven fabrics, knits or felts, and to theuse of these assemblies as catalyst and/or for recovering the preciousmetals.

BACKGROUND OF THE INVENTION

The industrial process for preparing nitric acid includes as essentialstep the oxidation of ammmonia into nitric oxide. This reaction isconducted industrially by passing a mixture of air and ammonia over ametal catalyst generally constituted by platinum or a platinum alloy.The precise conditions of reaction vary little from one installation tothe other; the mixture of 10% ammonia and 90% air by volume is preheatedto a temperature of 180°-250° C. before passage through the catalyst.The principal reaction:

    4NH.sub.3 +5 O.sub.2 →4 NO+6 H.sub.2 O

is effected during the time of contact with the catalyst, with a yieldwhich may attain 96%. This exothermic reaction raises the temperature ofthe gases and maintains the catalyst at 850°-900° C. The composition ofthe gases is such that there remains an excess of oxygen after reaction;in the range of temperatures attained, this oxygen forms with theplatinum a volatile oxide, which produces a loss of matter from thecatalytic cloths. These platinum losses vary, depending on the operatingconditions of the installations and are of the order of 50 to 400 mg ofplatinum per ton of nitric acid produced.

The metallic catalyst is generally in the form of cloths obtained byweaving linear threads. Numerous industrial installations, or burners,thus use platinum and rhodium alloys drawn into threads of 60 or 76 μmdiameter, then woven at a rate of 32 threads/cm warpwise and weftwise,to obtain a fabric comprising 1024 stitches/cm². A catalytic bed isconstituted by 3 to 40 superposed layers or cloths, this numberessentially depending on the operational pressure and the mass flowrateof the gases reduced to the surface unit of the catalytic bed. Thediameter of the catalytic cloths attains 5 m in certain burners.

The volatilized platinum may be partially picked up by means ofpalladium alloy cloths placed immediately beneath the layers of platinumcloths. These palladium alloy cloths are woven products, produced in thesame way as the catalytic cloths.

The same catalytic cloths are also employed by the synthesis ofhydrocyanic acid by the Andrussow process. The overall reaction is thefollowing:

    NH.sub.3 +CH.sub.4 +1.5 O.sub.2 →HCN+3 H.sub.2 O

This exothermic reaction raises the temperature of the gases to 1100° C.The operational conditions are such that there is no excess oxygen andthat platinum oxide cannot be formed; the level of the platinum lossesis, in this case, very low.

The form of embodiment of the platinum alloy catalysts has remained tothis day virtually identical to that developed at the beginning of the20th century. Certain improvements in the structure of the catalystshave been proposed, but they have not led to a long-lasting industrialexploitation.

French Patent 2 074 921 describes the replacement of about 1/3 to 2/3 ofthe precious metal cloths by a foraminous structure of non-preciousmetal, corrosion-resistant and such that the pressure drop is unchanged.This foraminous structure may be made in the form of a metal padconstituted by wires oriented at random.

European Patent 0 275 681 describes a catalyst pack comprising aforaminous layer of fibers of a metal of the platinum group or an alloycontaining same and at least one layer of foraminous ceramic materialhaving a coating of at least one of the metals of the platinum group.

French Patent 2 467 629 describes a catalytic bed which comprises anassembly or an agglomeration of fibers of a metal or an alloy of theplatinum group.

It should be noted that the examples described in these Patents presentthe common point of requiring the permanent use of one or more platinumcloths of the prior art to which novel structures are added; the novelstructures which are described in these Patents do not present acohesion and sufficient mechanical properties to be self-supporting. Theprocesses described make it possible to reduce the number of cloths ofthe prior art used, without being able to replace them entirely.

European Patent 0 364 153 describes the use of a knit obtained by aparticular process where the metal wire is associated with a yarn oftextile origin, the latter principally contributing an effect oflubrication; the latter is rendered necessary by the intense frictionsexerted on the yarn by the knitting machine hooks. The preparation ofknits by this process presents economical advantages, but alsodifficulties in obtaining knits which are sufficiently dense and whosestitches are as small as those of the cloths of the prior art. Themaximum width of the webs obtained is only 457 mm, which requires thewelding of numerous parallel webs to obtain pieces going up to adiameter of 5 m. Despite these drawbacks, knits are manufactured inaccordance with this process, industrially.

The conventional processes of manufacturing metallic cloths, wovenfabrics or knits use simple or linear threads. These processes presenttechnological limitations, encountered for example due to theinsufficient mechanical properties of certain metals whose threads breaktoo often during manufacture. They also present limitations ofprinciple, such as for example the impossibility of choosing the massper surface unit, the diameter of the threads and the number of stitchesper surface unit, independently.

SUMMARY OF THE INVENTION

The present invention makes it possible to overcome these drawbacks byreplacing the linear metal threads conventionally used by threadspreviously prepared in the form of helical elements.

The use of the threads according to the invention presents an essentialadvantage which is that of offering a considerable flexibility in thecreation of the finished products and of making available newconstructional parameters which were not accessible in the prior art. Inthe products containing the novel threads of the invention, it becomespossible to predetermine the mean mass per m² and the thickness of thefabric, independently, without alteration of the pressure drop presentedto the flow of the reagent gases.

The present invention makes it possible to produce novel structures ofcatalyst beds, by using the threads of novel structure hereinabove inreplacement of the simple or linear threads which constitute the fabricsof the prior art. Contrary to the majority of the products of the priorart, the products obtained by means of the novel threads according tothe invention present the advantage of necessitating no addition ofcloths of the prior art in order to be used in the industrialinstallations for manufacturing nitric acid.

The threads according to the invention are intended for manufacturingproducts such as metallic cloths, woven fabrics or knits, theseproducts, when they are principally constituted by precious metals,being usable as catalysts for manufacturing nitric acid, hydrocyanicacid, or as device for collecting the precious metals volatilized in thecourse of the reaction of manufacture of nitric acid.

Threads containing a helical winding of metal are already known. Forexample, French Patent 2 438 114 describes complex filiform textileelements intended to serve as substrate for a catalytic matter. Theseelements are constituted by a core of textile fiber of refractorymaterial and of metallic enveloping outer structure.

The helical windings described in French Patent 2 438 114 constitute ameans for improving the mechanical properties of certain fabrics ofrefractory fibers, of the type which are impregnated with catalyticsubstances to serve as catalyst in heating apparatus. The processdescribed consists in enveloping the fragile fibers by means of a metalthread which constitutes an outer armature. In this process, thequantity of metal thread, inert from the standpoint of catalysis, isselected to cover the surface of the fibers to be reinforced as littleas possible: the metallic reinforcement typically covers less than 10%of the surface of the fibers. The articles made according to thisprocess contain a small proportion of metal matter, which is contrary tothe purpose aimed at in the manufacture of catalysts for oxidation ofammonia and that the threads according to the invention make it possibleto attain.

Thus, according to a first aspect, the invention concerns a novel threadstructure containing at least one helical winding of at least one threadconstituted by a metal of the platinoid group or an alloy of such ametal.

It will be recalled that the group of platinoids, also called platinummine metals, is constituted by the following six metals: platinum,ruthenium, rhodium, palladium, osmium and iridium.

More precisely, according to one of its essential characteristics, theinvention concerns a thread comprising at least one helically woundfiliform element characterized in that it is constituted by a coreformed by at least one filiform element around which is helically woundat least one filiform element constituted by a metal of the platinoidgroup or an alloy of one of these metals.

Thus, the thread according to the invention is constituted by at leastone filiform element of which at least one is constituted by metal ofthe platinoid group or an alloy of one of these metals and is woundhelically.

However, insofar as this is not detrimental to the clarity of thedescription, each filiform element which itself constitutes a threadwill be designated hereinafter likewise by the word thread. It is onlywhen there is risk of confusion that the expression "filiform element"will be used.

According to another aspect of the invention, it relates to assemblingsof the above threads, in particular cloths, woven fabrics, knits, feltsobtained by different techniques such as weaving, knitting, sewing,embroidery.

According to a third aspect, the invention relates to the use of theassemblings of threads according to the invention as catalysts or asdevices for recovering the precious metals, in particular in chemicalprocesses employing said precious metals as catalysts.

DESCRIPTION OF THE DRAWINGS

The different aspects of the invention are illustrated in the followingdescription, given with reference to the different figures.

FIG. 1 shows the most simple structure of a thread according to theinvention comprising a core around which a thread is helically wound.

FIG. 2 shows a helical winding according to the invention after the corehas been eliminated.

FIG. 3 shows an embodiment of the thread according to the inventionwhere the core is constituted by several threads.

FIG. 4 shows another embodiment of the thread according to the inventionwhere one of the threads constituting the core has been eliminated.

FIG. 5 shows another embodiment of the thread according to the inventionwhere the core is constituted by an assembly of threads adapted to beeliminated and non-eliminated.

FIG. 6 reproduces by way of comparison, a photograph of a knit obtainedfrom a linear thread and described in comparative Example 14.

FIG. 7 reproduces a photograph of a knit obtained from a threadaccording to the invention and described in Example 15.

FIG. 8 reproduces a photograph of a knit obtained in accordance withExample 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

On a core or central thread, constituted by one or more threads ofdifferent nature or not, there is wound, with turns which are contiguousor not, at least one metal thread of the alloy or metal of which it isdesired to obtain the finished product.

FIG. 1 describes the most simple structure of a thread according to theinvention in which a thread 20 is helically wound around a thread 10constituting the core.

The thread 20 is constituted by the active matter necessary for thefinal use of the product, i.e. for example a platinum alloy in the caseof the final use being that of a catalyst, or a palladium alloy if thefinal use is the collection of the platinum volatilized in a catalyticprocess employing platinum or one of these alloys as catalyst.

Thread 10 may be:

either a thread of organic, natural or synthetic nature constituted by amatter adapted to be eliminated by dissolution, fusion or combustion,such as for example, cotton, linen, rayon, Nylon, polyester, fibers ofalginates,

a thread of an eliminatable matter of inorganic nature such as a metaleasily soluble in an acid, such as copper, silver, a metal soluble in abase, such as aluminium, or a meltable metal such as tin and leadalloys,

a thread of an inert, permanent matter in the final use, such as a steelor a refractory stainless alloy,

or a thread of active matter similar to that of thread 20.

Active matter similar to that of thread 20 is understood to mean a metalof the platinoid group or an alloy of one of these metals known for thesame catalytic activity in the reaction of manufacture of nitric acid orhydrocyanic acid or for making devices for recovering platinum duringthe manufacture of nitric acid. It may therefore be question of aplatinoid or an alloy of platinoid identical to or different from theone constituting thread 20.

The threads used for making the helical windings 20 of the threadsaccording to the invention are most often, at the start, in the form ofa linear thread, of circular section, with a diameter included between20 and 400 μm. The use of threads whose section is of different shape,such as circular threads rolled or crushed prior to use according to theinvention, also forms part of the invention. It is well known to the manskilled in the art that threads thus deformed present an increasedspecific surface, which favourably affects the catalytic activity.

When manufacturing the catalytic cloths of the prior art, the platinumalloy threads used have a diameter of between 50 and 90 μm, the mostwide-spread alloy compositions being the following: platinum alloyedwith 5% rhodium, platinum alloyed with 8% rhodium, platinum alloyed with10% rhodium, platinum alloyed with 5% rhodium and 5% palladium. Thesesame threads are the threads preferred for manufacturing the novelproducts for use as catalysts according to the invention, the turns ofthe novel threads having an outer diameter D_(e) included between 110and 1500 μm, obtained by effecting a winding on a core of diameterincluded between 10 and 1400 μm. The threads preferred for theconstruction of the catalytic products according to the invention havean outer diameter D_(e) included between 110 and 500 μm, obtained byeffecting a winding on a core of diameter included between 10 and 400μm.

When manufacturing cloths of the prior art for recovering thevolatilized platinum, the threads of palladium alloys used have adiameter of between 50 and 180 μm, the most wide-spread compositions ofalloys being the following: palladium alloyed with 5% copper, palladiumalloyed with 5% nickel, palladium alloyed with 5 to 20% gold. These samethreads are the preferred threads for manufacturing the novel productsaccording to the invention, for the use of recovery of the volatilizedplatinum, the turns of the novel threads having an outer diameter D_(e)included between included between 110 and 1500 μm, obtained by effectinga winding on a core of diameter included between 10 and 1400 μm. Thethreads preferred for the construction of the products according to theinvention intended for the recovery of the volatilized platinum have anouter diameter D_(e) included between 110 and 750 μm, obtained byeffecting a winding on a core whose diameter is included between 10 and650 μm.

In condensed manner, the threads according to the invention may also becharacterized in synthetic manner by the value of their mass per unit oflength, this value resulting from the choice of the precedinggeometrical parameters. Thus, the preferred threads according to theinvention are those whose mass per unit of length is included between1.5 and 5 times the mass of the linear thread employed in theirconstruction and which are obtained for example with a number of turnssuch that these turns cover 10% at minimum and 100% at maximum of thesurface of the threads of the core. The threads preferred for theconstruction of the catalytic products and the products intended forrecovering the volatilized platinum according to the invention have amass included between 1.8 and 3 times the mass of the linear threadcoming within their construction. The preferred threads according to theinvention are also such that the turns cover from 20 to 80% of thesurface of the threads of the core, which is also expressed by adistance between the turns included between 0.25 times and 4 times thediameter of the thread which constitutes the winding.

The thread 20, which constitutes the turns of a helix, is generally asingle one, but it may itself be composite, or the winding may beconstituted by a plurality of threads in parallel, possibly of differentnatures, which forms part of the invention. Moreover, thread 20, as wellas the other threads coming within the construction of a threadaccording to the invention, does not necessarily have a circularsection. It may be useful previously to draw a round thread to transformit into a tape which is used for thread 20; in that case, the threadmade according to the invention with such a tape presents a flattenedouter surface, which facilitates slide of this thread, such a propertybeing useful if the thread is used in a knitting machine.

FIG. 2 shows the appearance of a thread according to the invention,after elimination of the central thread by any process, leaving only thehelically wound thread of active matter. Such a thread is characterizedby its outer diameter "D_(e) ", by the diameter "d" of the initialthread, by the inner diameter "D" of the turns and by the pitch "p" ofthe winding which is the distance between the axes of two adjacentturns. Each of these parameters may be chosen freely, except for theouter diameter D_(e) which is worth D+2d; this freedom constitutes acharacteristic and an essential advantage of the invention, procuring awide latitude for the choice of the mass and the microgeometry of thethreads obtained according to the invention and the finished productsthat these threads produce.

Another advantage of the threads according to the invention is that theypresent novel properties facilitating use in the operations ofmanufacturing fabrics by weaving or by knitting; thus, the centralthread serving as support is the one which procures the characteristicsof tensile strength of the thread of the invention. The central threadmay, according to the invention, thus be chosen from the textile fibershaving a high elongation at rupture, much higher than that of simplemetal threads. The thread according to the invention will thus presentthe same characteristics of elongation as the textile thread, whilstincorporating in its structure the metal element which will give thefinished product the chemical properties sought as catalyst.

The thread prepared according to the invention allows manufacture ofcloths, woven fabrics, knits, by all techniques such as in particularweaving, knitting, sewing, embroidery, without having the fragility of amassive metal thread.

It may be chosen to eliminate the central thread before use of thefinished product, for example by decomposition, dissolution, fusion,oxidation, or to conserve it up to the instant of final use, whichrenders the cloths and knits according to the invention easy tomanipulate. Depending on the nature of the central thread and theconditions of final use, the central thread may be eliminated rapidly orslowly, and partially or totally.

If it is chosen to eliminate the central thread, the fabric obtained,constituted solely by helical threads, is exaggeratedly elastic anddeformable, the turns being able to be drawn easily. Such a fabric lacksrigidity to such a point that it becomes difficult to manipulate withoutundergoing deformations. To overcome this drawback, one arrangement ofthe invention consists in introducing an additional thread in thecentral core, jointly with the thread of eliminatable matter.

This arrangement, which forms part of the invention, is illustrated inFIG. 3 where the core is constituted by threads 10 and 11, on which iswound thread 20, each of threads 10 and 11 being able to be:

either a thread of an eliminatable matter of organic, soluble, meltableor combustible nature, such as a textile fiber,

a thread of an eliminatable matter of inorganic nature, such as a metalwhich is easily soluble, meltable or oxidizable,

a thread of a matter which is inert and permanent in the final use, suchas steel or a refractory stainless alloy,

or a thread of active matter similar to that of thread 20, thread 20being constituted by the active matter necessary for the final use ofthe product, i.e. for example a platinum alloy in the case of the finaluse being that of a catalyst, or a palladium alloy if the final use isthe collection of the platinum volatilized in the course of a catalyticprocess employing platinum or a platinum alloy as catalyst.

We have observed that a thread according to the invention prepared inaccordance with the above arrangement, conserves the novel mechanicalproperties contributed by the invention, namely the characteristic oftensile strength remain those of the most resistant thread introduced inthe core of the thread.

FIG. 4 illustrates the case of the thread 11 having been chosen from theeliminatable matters and where it has been eliminated by an appropriateprocess. The product obtained, which forms part of the invention, is nowconstituted only by the thread 20 in helical form including in its innerspace the thread 10. In this state, the thread 20, free of anyconstraints, may be freely positioned in the whole available spacereleased by the elimination of thread 11.

It also results from the invention, whereby a thread is prepared,comprising a helical element in the inner space of which a linear threadmay be located, that the products, fabrics or knits, prepared with sucha thread, present an exceptional behaviour with respect to deformations.In fact, in the case of an effort of traction exerted on a fabriccausing rupture of the threads, a fabric of the prior art presents atear which is an opening through which the reagent gases may passwithout contact with the catalytic matter; this is translated by a lossof reaction yield which may lead to stoppage of the exploitation. Afabric prepared with a thread of the invention does not present thisdrawback; in the case of excessive effort exerted on the fabric, thereis firstly produced rupture of the linear threads, if they are present;but the helical threads are only drawn. According to the manufacturingcharacteristics, such as diameter of the core and pitch of the turns,the helical threads may thus be drawn by several times their lengthwithout breaking. The consequence of this is that a fabric prepared witha thread of the invention and subjected to excessive efforts of tractionis locally drawn without creating an opening allowing passage of thereaction gases without contact with the active or catalytic matter.

In the case of manufacture in the form of a knit, the preceding threadmay be used, comprising a reinforcing thread in the central core. It isalso possible to use a helical thread with eliminatable core accordingto the invention and simultaneously to supply the knitting machine withthis thread and a linear reinforcing thread which may be metallic. Inthat case, in the finished product, the reinforcing thread will at allpoints be parallel to the axis of the helical thread according to theinvention, but outside the helix.

In the two examples above, the linear thread makes it possible toreinforce the knit produced.

According to another embodiment of knits according to the invention, aknit may be produced by means of a linear thread, and a helical threadaccording to the invention inserted between the stitches of this knit.Such a composite knit presents the advantage of being able to beproduced in one sole operation by using, for example, a circularknitting machine provided with two thread supply devices.

In such composite knits, the linear thread used may either be a threadof platinoid or platinoid alloy of nature identical to that used for thehelical winding, or a thread of refractory material inert at thetemperature of use of the catalyst.

In the case of weaving, it suffices to introduce a proportion of linearthreads among the threads according to the invention, this proportionbeing able to be different in the warp and in the weft.

These linear threads are constituted either by threads of platinoid orplatinoid alloy of the same type as those used for effecting the helicalwinding, or by threads constituted by a refractory alloy.

The use of a helical thread whose core contains a linear reinforcingthread is also part of the invention, and such embodiments are describedin the Examples hereinafter.

FIG. 5 schematically shows the case of a thread according to theinvention whose core is constituted by a plurality of threads, herethree threads 10, 11, 12, possibly of different nature, certain beingable to be eliminated and others not.

It is also possible according to the invention, previously tomanufacture the central thread in a more elaborate form, such as astrand of eliminatable threads and non-eliminatable threads.

Another variant of threads according to the invention in which the coreof the thread is formed both of eliminatable and non-eliminatablematerial, consists in using, as thread constituting the core of thethread of the invention, a thread constituted by a non-eliminatablematter coated with an eliminatable matter, the coating being able to beobtained by any process such as varnishing, coating, electrophoresis,galvanic deposit, by which a thread of a non-eliminatable matter iscoated with an eliminatable matter.

The following Examples are given purely by way of illustration of theinvention and its advantages.

EXAMPLES

With a view to illustrating the present invention, in non-limitingmanner, some descriptive examples of practical embodiment of the threadsobtained and their uses, are given hereinbelow.

Examples 1 to 6 demonstrate an essential advantage of the inventionwhich is the freedom in the choice of the mass and of the geometry ofthe threads. Similarly, the practical production of the fabrics ofExamples 7 to 12 demonstrates that this advantage also exists for theproducts manufactured with the threads of the invention. The threadsaccording to the invention make it possible to obtain, by way ofexample, fabrics of which the mass per m² is from 1.25 to 3 timesgreater than that of the cloths of the prior art, these limits being inno wise that of the invention. This advantage is obtained by employingthe same threads as those which constitute the cloths of the prior art,and by incorporating them as filiform elements to show at least onehelical element constituting the threads according to the invention.

Another property of the threads of the invention when they are employedin the weaving technique is that they allow several possibleconstructions to obtain the same mass per m² of the finished products.This property is illustrated by Examples 9 and 12 which concern themanufacture of cloths whose mass per m² is close to 1100 g. Example 9uses a warp comprising 32 threads/cm, whilst in Example 12, the warpcomprises only 16 threads/cm, the weft threads always being at 24/cm;the lesser quantity of matter in the warp is compensated by using aheavier thread weftwise, such increase in mass of the weft thread havingbeen obtained by increasing the number of turns to the cm in thepreparation of the weft thread according to the invention. This propertyconstitutes an advantage contributed by the threads of the invention tothe weaving technique, as they make it possible to reduce the number ofthe warp threads and therefore substantially to reduce the warp assemblytime and therefore the manufacturing costs.

This embodiment of the threads according to the invention, which has theapparent effect of increasing the quantity of matter present in each m²of fabric, is not translated by a reduction in the transparency and anincrease in the pressure drop, as would occur by increasing the numberof threads of a fabric of the prior art. The specific property that thethreads according to the invention procure is that they make it possibleto prepare thicker products than those which are obtained by weavinglinear threads; in fact, the products made become veritablythree-dimensional, their thickness being able to be chosen freely fromthe value of the diameter "D" of the core serving for the winding. Whenweaving fabrics of the prior art, the thickness depends only on thediameter of the threads, the mechanical tension applied during weavingand on the weaving pattern: the thickness of a fabric of the prior artis twice the diameter of the threads in straight weaving and about threetimes the diameter of the threads in herringbone weaving.

The practical embodiment of the fabrics of Examples 8 to 12 has made itpossible to discover two other advantages of the products according tothe invention over the products of the prior art.

A novel property of the fabrics prepared with the threads of theinvention is that they present an increased rigidity which renders verydifficult their deformation in the sense of the bisectrices of thedirections of the warp threads and of the weft threads, whilst this typeof deformation is very easy with the fabrics of the prior art. Thisproperty results in that a circular cloth according to the invention hasthe advantage of conserving its circular shape after handlings, whilst acloth of the prior art manipulated without precautions easily becomesoval.

This property is the consequence of the imbrication of the warp threadswhich are linear threads in our Examples, between the turns of the weftthreads, which are helical threads according to the invention.

The second advantage precisely concerns the contact between the reagentgases and the threads of active matter. In a cloth of the prior art,there are numerous points of intersection with punctual contact betweenthe weft threads and the warp threads; there is exactly one intersectionof threads per stitch, these stitches being most usually 1024/cm² innumber, when the cloth comprises 32 warp threads and 32 weft threads/cm.It is well known to the man skilled in the art that an examination ofthe worn catalytic cloths with a scanning microscope reveals that thepoints of intersection and the close zone which surrounds them areregions hardly active from the standpoint of catalysis as these zonesconstitute anfractuosities in which the reagent gases only diffuse withdifficulty. In a cloth of the prior art, the intersections of threadsare therefore hardly active zones which contain a fraction of surface ofthe threads which remains hardly or not useful on contact of the gaseswith the threads.

In a cloth woven with a thread according to the invention, comprising anelement in helical form, the intersections of threads, referred to theunit of mass, are less numerous, at equal meshing, than in a cloth ofthe prior art; this is simply due to the fact that the helix turnsincluded between two intersections represent a larger quantity of matterthan the simple linear thread which would replace this helix. Moreover,the use of the threads according to the invention allows a reduction inthe number of the warp threads and of the weft threads, whilst making itpossible to manufacture denser fabrics than the fabric of the prior art,as Examples 7 to 11 show. It follows that the threads according to theinvention allow a considerable reduction in the number of effectivepoints of intersection between threads, and therefore better use of thesurface of the threads used. Moreover, in the case of products wovenwith threads of the invention, the geometrical orientation of the pointsof intersection between threads is different from that which ispresented by the prior products; in fact, in the prior products, thepoints of intersection always lie beneath a thread, which creates aneffect of shading and renders them hardly accessible to the gaseouscurrent which must surround this thread; in a fabric containing threadsof the invention for weft threads and linear threads for the warp, theorientation of the helix turns is almost orthogonal with respect to thepreceding case; it follows that the points of intersection of threadspresent their opening directly in the direction of the gaseous currentand that they may therefore be more efficient for the contacts with thereaction gases.

In summary, the threads according to the invention allow a reduction inthe density of the points of intersection, referred to the unit of mass,as well as an improvement in the circulation of the gases in theremaining points of intersection. These properties are togethertranslated by an increase in the surface available for the exchangeswith the gaseous phase, as well as by an improvement in the diffusiontowards this surface, with the consequence for the final use of asubstantial increase in the catalysis yield and an increase in the lifeduration of the catalytic cloths. In the case of applying the threads ofthe invention to the cloths of palladium alloy used for collecting thevolatilized platinum, the advantage procured is an improved efficiencyof collection.

Furthermore, Example 15 clearly shows the specific gain in mass obtainedfor a composite knit made by associating a simple thread and a threadaccording to the invention with respect to the knit obtained on the samemachine with a simple linear thread and described in Comparative Example14.

The present invention is applicable to the preparation of felts, wovenfabrics, knits or any assemblings of threads of precious metals andalloys thereof which are used as catalytic mass for the manufacture ofnitric acid, or hydrocyanic acid, or as device for collecting theprecious metals volatilized during these reactions.

EXAMPLE 1

A thread of platinum alloy with 8% rhodium, with a diameter of 76 μm,which has a mass of 92 mg/m, is wound around a thread of cotton ofcaliber 60 at a rate of 70 turns/cm. The thread obtained has a diameterof 320 μm and a mass of 450 mg/m comprising 36 mg of cotton per meter.

EXAMPLE 2

A thread of palladium alloy with 5% copper, with a diameter of 76 μm,which has a mass of 53 mg/m, is wound around a thread of cotton ofcaliber 60 at a rate of 70 turns/cm. The thread obtained has a diameterof 320 μm and a mass of 320 mg/m, comprising 36 mg of cotton per meter.

EXAMPLE 3

A thread of cotton of caliber 60 and a thread of platinum alloy with 8%rhodium, with a diameter of 76 μm, are disposed in parallel. A secondthread of platinum alloy with 8% rhodium, of 76 μm diameter, is woundaround the two preceding threads at a rate of 70 turns/cm. The threadobtained has a flattened profile; its apparent diameter is from 300 to350 μm and its mass is 570 mg/m, comprising 36 mg of cotton per meter.

EXAMPLE 4

A thread of cotton of caliber 60 and a thread of palladium alloy with 5%copper, with a diameter of 76 μm, which has a mass of 53 mg/m, aredisposed in parallel. A second thread of palladium alloy with 5% copper,of 76 μm diameter, is wound around the two preceding threads at a rateof 70 turns/cm. The thread obtained has a flattened profile; itsapparent diameter is from 300 to 350 μm and its mass is 380 mg/m,comprising 36 mg of cotton per meter.

EXAMPLE 5

A thread of cotton of caliber 60 and a thread of platinum alloy with 8%rhodium, with a diameter of 76 μm, are disposed in parallel. A secondthread of platinum alloy with 8% rhodium, with a diameter of 76 μm, iswound around the two preceding threads at a rate of 35 turns/cm. Thethread obtained has a diameter of 300 μm and a mass of 400 mg/m,comprising 36 mg of cotton per meter.

EXAMPLE 6

A thread of cotton of caliber 60 and a thread of palladium alloy with 5%copper, with a diameter of 76 μm, which has a mass of 53 mg/m, aredisposed in parallel. A second thread of palladium alloy with 5% copper,with a diameter of 76 μm, is wound around the two preceding threads at arate of 35 turns/cm. The thread obtained has a flattened profile; itsapparent diameter is from 300 to 350 μm and its mass is 230 mg/m,comprising 36 mg of cotton per meter.

Examples 1 to 6 demonstrate the first essential advantage of theinvention, which is that of procuring a considerable freedom ofconstruction by the choice of the mass and the microgeometry of thethreads that the invention produces, as a function of the outer diameterD_(e), the diameter "d" of the initial thread, the inner diameter "D" ofthe turns, determined by the structure of the central thread and of thepitch "p" of the winding which is the distance between the axes of twoadjacent turns.

A preferred industrial method for manufacturing the threads described inthe Examples is the use of a wrapping machine. However, this preferredmethod is in no way limiting, the threads according to the inventionalso being able to be obtained by other processes such as winding on amandrel; in that case, the helix obtained is disengaged by sliding outof the mandrel as it is formed. A hollow mandrel may make it possible tointroduce one or more threads inside the helix, without these threadsserving as winding support.

To complete the illustration of the present invention, in non-limitingmanner, some descriptive Examples of practical embodiment of thefinished products which may be manufactured by means of the novelthreads according to the invention, are given hereinbelow.

EXAMPLE 7

The thread of Example 3, constituted by a thread of platinum alloy with8% rhodium, with a diameter of 76 μm, wound at a rate of 70 turns/cmaround a thread of cotton and by a thread of platinum alloy with 8%rhodium, with a diameter of 76 μm, is used for manufacturing a fabric,by means of a manual weaving loom.

In this way, a woven cloth is produced, comprising warp threads distantby 6.35 mm and contiguous weft threads. A disc of 70 mm diameter of thisfabric contains a mass of precious metals of 7.0 g, or a mass of 1820g/m². By way of comparison, the fabric of the prior art prepared withthe same thread, which is woven with 32 threads/cm warpwise andweftwise, and which comprises 1024 stitches/cm², has a mass of 620 g/m².

The fabric of this Example, prepared by means of a thread according tothe invention, may be used as catalytic cloth in an ammonia oxidationinstallation, replacing 3 cloths of the prior art.

EXAMPLE 8

The thread of Example 5, constituted by a thread of platinum alloy with8% rhodium, with a diameter of 76 μm, wound at a rate of 35 turns/cmabout a thread of cotton and by a thread of platinum alloy with 8%rhodium, with a diameter of 76 μm, is used for manufacturing a fabric,by means of an industrial weaving loom 2.50 m wide.

The thread according to the invention is used as weft thread, the warpthreads being simple threads, of the same alloy, 76 μm diameter. Thefabric obtained comprises 32 warp threads/cm and 24 weft threads/cm. Theaverage mass of this fabric is 1211 g/m², viz. 95% more than the mass of620 g/m² of the fabric of the prior art prepared with the same thread,and woven with 32 threads/cm warpwise and weftwise. The thickness of thefabric obtained with the thread of the invention is 340 μm, whilst thefabric of the prior art has a thickness of 210 μm, slightly more thandouble the diameter of the threads.

The fabric of this Example prepared by means of a thread according tothe invention may be used as catalytic cloth in an ammonia oxidationinstallation, replacing 2 cloths of the prior art.

EXAMPLE 9

The thread of Example 5, constituted by a platinum alloy with 8%rhodium, 76 μm diameter, wound at a rate of 35 turns/cm around a threadof cotton and by a thread of platinum alloy with 8% rhodium, 76 μmdiameter, is used for manufacturing a fabric, by means of an industrialweaving loom 2.50 m wide.

The thread according to the invention is used as weft thread, the warpthreads being simple threads, of the same alloy, 76 μm diameter. Thefabric obtained comprises 32 warp threads/cm and 21 weft threads/cm. Theaverage mass of this fabric is 1098 g/m², viz. 77% more than the mass of620 g/m² of the fabric of the prior art prepared with the same thread,and woven with 32 threads/cm warpwise and weftwise. The thickness of thefabric obtained with the thread of the invention is 340 μm, whilst thefabric of the prior art has a thickness of 210 μm, slightly more thandouble the diameter of the threads.

The fabric of this Example, prepared by means of a thread according tothe invention, may be used as catalytic cloth in an ammonia oxidationinstallation, 2 thicknesses of this novel fabric being able to replace 2cloths of the prior art.

EXAMPLE 10

The thread of Example 6, constituted by a thread of palladium alloy with5% copper, 76 μm diameter, wound at a rate of 35 turns/cm around athread of cotton and by a thread of palladium alloy with 5% copper, 76μm diameter, is used for manufacturing a fabric by means of anindustrial weaving loom 2.50 m wide.

The thread according to the invention is used as weft thread, the warpthreads being simple threads, of the same alloy, 76 μm diameter. Thefabric obtained comprises 32 warp threads/cm and 19 weft threads/cm. Theaverage mass of this fabric is 575 g/m², viz. 47% more than the mass of390 g/m² of the fabric of the prior art woven with 32 threads/cmwarpwise and weftwise, prepared with the same thread. The thickness ofthe fabric obtained with the thread of the invention is 340 μm, whilstthe fabric of the prior art has a thickness of 210 μm, slightly morethan double the diameter of the threads.

The fabric of this Example, prepared by means of a thread according tothe invention, may be used as cloth for recovering the volatilizedplatinum in an ammonia oxidation installation, its capacity ofabsorption of platinum being about 1.5 times that of a cloth of theprior art.

Examples 7 to 10 above describe embodiments of products using threads ofthe invention and, apart from a thread of cotton, including onlyprecious metals of homogeneous composition. It is also possible tocreate products including threads of precious metals according to theinvention associated with threads of common metals, as shown by Example11 in descriptive and non-limiting manner.

EXAMPLE 11

The thread of Example 5, constituted by a thread of platinum alloy with8% rhodium, 76 μm diameter, wound at a rate of 35 turns/cm around athread of cotton and by a thread of platinum alloy with 8% rhodium, 76μm diameter, is used for manufacturing a fabric by means of anindustrial weaving loom 2.50 m wide.

The thread according to the invention is used as weft thread, the warpthreads being simple threads, of a refractoy alloy such as Kanthal(Registered Trademark of the firm Bulten-Kanthal AB), 60 μm diameter.The fabric obtained comprises 16 warp threads/cm and 21 weft threads/cm.The average mass of this fabric is 822 g/m², decomposing into 788 g ofthreads of platinum alloy with 8% rhodium and 34 g of threads ofrefractory alloy. The catalytically active part of this fabric, namelythe 788 g of threads of plating alloy with 8% rhodium, represent a massper m² greater by 27% than the mass of 620 g/m² of the fabric of theprior art prepared with the same thread and woven with 32 threads/cmwarpwise and weftwise. The thickness of the fabric obtained with thethread of the invention is 340 μm, whilst the fabric of the prior arthas a thickness of 210 μm, slightly more than double the diameter of thethreads.

The fabric of this Example prepared by means of a thread according tothe invention to which is added a refractory thread, may be used ascatalytic cloth in an ammonia oxidation installation, 4 thicknesses ofthis novel fabric being able to replace 5 cloths of the prior art.

EXAMPLE 12

A thread according to the invention is constituted by a thread ofplatinum alloy with 8% rhodium, 76 μm diameter, wound at a rate of 42turns/cm around a thread of cotton and by a thread of platinum alloywith 8% rhodium, of 76 μm diameter; its mass is 480 mg/m. It is used formanufacturing a fabric, by means of an industrial weaving loom 2.50 m inwidth.

The thread according to the invention is used as weft thread, the warpthreads being simple threads, of the same alloy, 76 μm diameter. Thefabric obtained comprises 16 warp threads/cm and 21 warp threads/cm. Theaverage mass of this fabric is 1092 g/m², viz. 76% more than the mass of620 g/m² of the fabric of the prior art prepared with the same thread,and woven with 32 threads/cm warpwise and weftwise. The thickness of thefabric obtained with the thread of the invention is 340 μm, whilst thefabric of the prior art has a thickness of 210 μm, slightly more thandouble the diameter of the threads.

The fabric of this Example, prepared by means of a thread according tothe invention, may be used as catalytic cloth in an ammonia oxidationinstallation, 2 thicknesses of this novel fabric being able to replace 3cloths of the prior art.

EXAMPLE 13

The thread of Example 5, constituted by a thread of platinum alloy with8% rhodium, 76 μm diameter, wound at a rate of 25 turns/cm around athread of cotton and by a thread of platinum alloy with 8% rhodium, 76μm diameter, is used for manufacturing a knit by means of an industrialknitting machine with a diameter of 600 mm.

The thread according to the invention is used as single thread forsupplying this machine, which comprises 12 needles/cm. The tubular knitobtained has a flat width of 1880 mm, it comprises 12 stitches/cm and 9rows/cm, viz. 108 stitches per cm². The average mass of this knit is 780g/m², viz. 26% more than the mass of 620 g/m² of the fabric of the priorart prepared with the same thread, and woven with 32 threads/cm warpwiseand weftwise. The thickness of the knit obtained with the thread of theinvention is 700 μm, whilst the fabric of the prior art has a thicknessof 210 μm, slightly more than double the diameter of the threads.

The fabric of this Example, prepared by means of a thread according tothe invention, may be used as catalytic cloth in an ammonia oxidationinstallation, 3 thicknesses of this novel fabric being able to replace 4cloths of the prior art.

EXAMPLE 14 (Comparative)

A simple thread of platinum alloy with 5% rhodium, with 76 μm diameter,is used for supplying a circular knitting machine with a diameter of 700mm, equipped with gauge 24 needles. The mechanism of this machine isadapted to obtain the simplest knit, or jersey.

The use of 1250 g of thread made it possible to obtain a tubular knit2.21 m long and with a diameter of 650 mm representing a surface of 4.52m². The photograph reproduced in FIG. 6 shows the macrostructure of thisknit magnified 25 times. The specific mass of this knit is 276 g/m² Byway of comparison, the fabric of the prior art prepared with the samethread, which is woven with 32 threads per cm warpwise and weftwise, andwhich comprises 1024 stitches per cm² has a mass of 620 g/m².

EXAMPLE 15

A simple thread of platinum alloy with 5% rhodium, with a diameter of 76μm, is used in the same way as in Example 14 for supplying a circularknitting machine with a diameter of 700 mm, equipped with gauge 24needles.

Furthermore, a thread according to the invention is prepared in thefollowing manner: 2 threads of cotton of caliber 60 are disposed inparallel. A thread of platinum alloy with 5% rhodium, of 76 μm diameter,is wound around the two preceding threads at a rate of 35 turns per cm.The thread obtained has a mean diameter of 300 μm and a mass of 295 mgper meter, comprising 72 mg of cotton.

The knitting machine is provided with a second supply device whichreceives the thread according to the invention: under these conditions,it is possible to obtain a composite knit associating the simple thread,which constitutes a network disposed according to the description ofExample 14, and the thread according to the invention, which is insertedbetween the meshes of the preceding network. The photograph reproducedin FIG. 7 shows the macrostructure of the knit obtained, magnified 25times, after the threads of cotton included in the thread according tothe invention have been eliminated by combustion. The specific mass ofthis knit is 645 g/m², composed of 276 g/m² of simple thread arranged injersey form as described in Example 14 and of 369 g/m² of threadaccording to the invention which are disposed in parallel at a rate of15 threads per cm.

The knit obtained in this Example has a specific mass very close to thatof a fabric of the prior art prepared with the same thread, which iswoven with 32 threads per cm warpwise and weftwise, to attain a mass of620 g/m².

EXAMPLE 16

A simple thread of an alloy for electrical resistors such as GILPHY 70(Registered Trademark of the firm IMPHY), with a diameter of 80 μm and amass of 41 mg per meter, is used in the same manner as in Example 14 forsupplying a circular knitting machine with a diameter of 700 mm,equipped with gauge 24 needles.

Furthermore, a thread according to the invention is prepared in thefollowing manner: 2 threads of cotton of caliber 60 are disposed inparallel. A thread of platinum alloy with 5% rhodium, of 76 μm diameter,is wound around the two preceding threads at a rate of 55 turns per cm.The thread obtained has a mean diameter of 300 μm and a mass of 405 mgper meter, comprising 72 mg of cotton.

The knitting machine is provided with a second supply device whichreceives the thread according to the invention: under these conditions,it is possible to obtain a composite knit associating the simple thread,which constitutes a network arranged according to the description ofExample 14, and the thread according to the invention, which is insertedbetween the meshes of the preceding network. The photograph reproducedin FIG. 8 shows the macrostructure of the knit obtained, magnified 25times, after the threads of cotton included in the thread of theinvention have been eliminated by combustion; this macrostructure isidentical to that of Example 15. The specific mass of this knit is 703g/m², composed of 123 g/m² of GILPHY 70 thread arranged in jersey formas described in Example 14, and 580 g/m² of thread of platinum alloywith 5% rhodium according to the invention which are disposed inparallel at a rate of 15 threads per cm.

The knit obtained in this Example has a specific mass in precious metalcontained therein very close to that of a fabric of the prior artprepared with the same thread, which is woven with 32 threads per cmwarpwise and weftwise, to attain a mass of 620 g/m².

We claim:
 1. A wire comprising a helical winding made of at least onefirst thread which is helically wound around at least one second threadconstituting the core of said wire, wherein the helical windingcomprises at least one first thread made of material selected from thegroup consisting of the metals of the platinoid group and alloysthereof.
 2. The wire according to claim 1, wherein said core comprisesat least one thread made of a material adapted to be removed bydissolution, melting or combustion.
 3. The wire according to claim 1,wherein said core is comprised of a material which is chemically inert.4. The wire according to claim 1, wherein the core comprises at leastone thread made of material selected from the group consisting of themetals of the platinoid group and alloys thereof.
 5. The wire accordingto claim 1, wherein the helical winding comprises at least one threadmade of platinum or of a platinum alloy.
 6. The wire according to claim1, wherein the helical winding comprises at least one thread made ofpalladium alloy.
 7. The wire according to claim 1, wherein the helicalwinding is comprised of a plurality of parallel threads of which atleast one is comprised of a material selected from the group consistingof the metals of the platinoid group and alloys thereof.
 8. The wireaccording to claim 1, wherein the mass per unit of length of said wireis between 1.5 and 5 times the mass of said first thread.
 9. The wireaccording to claim 1, wherein the helical winding is comprised of aplurality of turns and the distance between two consecutive turns of thehelical winding is between 0.25 and 4 times the diameter of said firstthread.
 10. An assembling of wires wherein said assembling ismanufactured by a technique selected from the group consisting ofweaving, knitting, sewing and embroidery techniques and comprises atleast one wire comprising at least one helically wound thread made of amaterial selected from the group consisting of the metals of theplatinoid group and alloys thereof.
 11. The assembling according toclaim 10 wherein said wire further comprises a core around which saidthread is helically wound.
 12. The assembling according to claim 11,wherein the core comprises at least one thread made of a materialselected from the group consisting of the metals of the platinoid groupand alloys thereof.
 13. The assembling according to claim 10, whereinthe helical winding comprises at least one thread made of platinum or ofa platinum alloy.
 14. The assembling according to claim 10, wherein thehelical winding comprises at least one thread made of palladium alloy.15. The assembling according to claim 10, wherein the helical winding iscomprised of a plurality of parallel threads of which at least one iscomprised of a material selected from the group consisting of the metalsof the platinoid group and alloys thereof.
 16. The assembling accordingto claim 10, wherein the mass per unit of length of said helical windingis between 1.5 and 5 times the mass of said first thread.
 17. Theassembling according to claim 10, wherein the distance between twoconsecutive turns of the helical winding is between 0.25 and 4 times thediameter of said first thread.
 18. The assembling of wires according toclaim 10 wherein said assembling is a knit manufactured by a knittingtechnique.
 19. The assembling according to claim 10, wherein said wirecomprising a helical winding is inserted between the stitches of a knitcloth which is manufactured by knitting a linear thread.
 20. Theassembling according to claim 19, wherein said linear thread is made ofa material selected from the group consisting of metals of the platinoidgroup, platinoid alloys and refractory materials.
 21. The assemblingaccording to claim 10, wherein said assembling is manufactured by aweaving technique.
 22. The assembling according to claim 21, wherein thewires comprising helically wound threads represent only a part of thethreads used for manufacturing said weave, the other threads beingcomprised of linear threads intended to ensure reinforcement of thewoven product.
 23. A device acting as a catalyst wherein said devicecomprises an assembling of wires manufactured by a technique selectedfrom the group consisting of weaving, knitting, sewing and embroiderytechniques and comprising at least one wire comprising at least onehelically wound thread made of a material selected from the groupconsisting of the metals of the platinoid group and alloys thereof. 24.The device according to claim 23 wherein said at least one wire furthercomprises a core around which said thread is helically wound.
 25. Thedevice according to claim 24, wherein the core comprises at least onethread made of a material selected from the group consisting of themetals of the platinoid group and alloys thereof.
 26. The deviceaccording to claim 23, wherein the helical winding comprises at leastone thread made of platinum or of a platinum alloy.
 27. The deviceaccording to claim 23, wherein the helical winding is comprised of aplurality of parallel threads of which at least one is comprised ofconstituted by a material selected from the group consisting of themetals of the platinoid group and the alloys thereof.
 28. The deviceaccording to claim 23, wherein the mass per unit of length of saidhelical winding is between 1.5 and 5 times the mass of said at least onethread.
 29. The device according to claim 23, wherein the distancebetween two consecutive turns of the helical winding is between 0.25 and4 times the diameter of said at least one thread.
 30. The deviceaccording to claim 23 wherein said device is manufactured by a knittingtechnique.
 31. The device according to claim 23, wherein said wirecomprising a helically winding is inserted between the stitches of aknit manufactured by knitting a linear thread.
 32. The device accordingto claim 31, wherein said linear thread is made of a material selectedfrom the group consisting of metals of the platinoid group, platinoidalloys and refractory materials.
 33. The device according to claim 23,wherein said device is manufactured by a weaving technique.
 34. Thedevice according to claim 33, wherein the wires comprising helicallywound threads represent only a part of the threads used formanufacturing said weave, the other threads being constituted by linearthreads intended to ensure reinforcement of the woven product.
 35. Thedevice according to claim 23, acting as a catalyst and destined to thereaction of oxidation of ammonia into nitrogen oxide with a view topreparing nitric acid or to the reaction of preparation of hydrocyanicacid, wherein the helically wound thread is a thread of platinum orplatinum alloy.
 36. A device for recovering particles of precious metalsor alloys thereof used as catalysts of chemical reactions wherein saiddevice comprises an assembling of wires manufactured by a techniqueselected from the group consisting of weaving, knitting, sewing andembroidery techniques and comprising at least one thread comprising atleast one helically wound wire made of material selected from the groupconsisting of the metals of the platinoid group and alloys thereof. 37.The device according to claim 36 wherein said wire further comprises acore around which said thread is helically wound.
 38. The deviceaccording to claim 37, wherein the core comprises at least one threadmade of a material selected from the group consisting of the metals ofthe platinoid group and alloys thereof.
 39. The device according toclaim 36, wherein the helical winding comprises at least one thread madeof palladium or of a palladium alloy.
 40. The device according to claim34, wherein the helical winding is comprised of a plurality of parallelthreads of which at least one is comprised of a material selected fromthe group consisting of the metals of the platinoid group and alloysthereof.
 41. The device according to claim 36, wherein the mass per unitof length of said helical winding is between 1.5 and 5 times the mass ofsaid at least one thread.
 42. The device according to claim 36, whereinthe distance between two consecutive turns of the helical winding isbetween 0.25 and 4 times the diameter of said at least one thread. 43.The device according to claim 36 wherein said device is manufactured bya knitting technique.
 44. The device according to claim 36, wherein saidwire comprising a helical winding is inserted between the stitches of aknit manufactured by knitting a linear thread.
 45. The device accordingto claim 44, wherein said linear thread is made of a material selectedfrom the group consisting of metals of the platinoid group, platinoidalloys and refractory materials.
 46. The device according to claim 36,wherein said device is manufactured by a weaving technique.
 47. Thedevice according to claim 46, wherein the wires comprising helicallywound threads represent only a part of the threads used formanufacturing said weave, the other threads being comprised of linearthreads intended to ensure reinforcement of the woven product.
 48. Amethod of using a catalyst in a chemical reaction which comprisesproviding a catalyst that is comprised of an assembling of wirescomprising at least one wire that includes a helically wound thread madeof a material selected from the group consisting of the metals of theplatinoid group and alloys thereof, and using said catalyst in order toperform said chemical reaction.
 49. A method of using a catalystaccording to claim 48 wherein the mass per unit of length of saidhelical winding is between 1.5 and 5 times the mass of said firstthread.
 50. A method of using a catalyst according to claim 48 whereinthe distance between two consecutive turns of the helical winding isbetween 0.25 and 4 times the diameter of said first thread.
 51. A methodof using a catalyst according to claim 48 wherein said helically woundthread is made of a material selected from the group consisting ofplatinum, a platinum alloy, palladium and a palladium alloy.
 52. Amethod of using a device for recovering particles of precious metals oralloys thereof used as catalysts of chemical reactions which comprisesproviding a device that is comprised of an assembling of wirescomprising at least one wire that includes a helically wound thread madeof a material selected from the group consisting of the metals of theplatinoid group and alloys thereof, and using said device for recoveringsaid particles.
 53. A method of using a device for recovering particlesaccording to claim 52 wherein the mass per unit of length of saidhelical winding is between 1.5 and 5 times the mass of said firstthread.
 54. A method of using a device for recovering particlesaccording to claim 52 wherein the distance between two consecutive turnsof the helical winding is between 0.25 and 4 times the diameter of saidfirst thread.
 55. A method of using a device for recovering particlesaccording to claim 52 wherein said helically wound thread is made of amaterial selected from the group consisting of palladium and a palladiumalloy.
 56. A method according to claim 48 wherein said assemblying ofwires is manufactured by a technique selected from the group consistingof weaving, knitting, sewing and embroidery.
 57. A method according toclaim 52 wherein said assemblying of wires is manufactured by atechnique selected from the group consisting of weaving, knitting,sewing and embroidery.